Electric power plant system and method for operating a steam turbine especially of the nuclear type preferably with electronic reheat control and an electronic reheater

ABSTRACT

An electronic system is provided for operating an electric power plant of the nuclear type with an electronic steam reheating control system applied to the nuclear turbine system which operates in response to low pressure turbine temperatures. The control system is adapted to operate in a plurality of different automatic control modes to control reheating steam flow and other steam parameters, each of such modes of control permitting turbine temperature variations within predetermined constraints and according to predetermined functions of time.

United States Patent 1 91 Luongo et a1.

154] ELECTRIC POWER PLANT SYSTEM AND METHOD FOR OPERATING A STEAM TURBINE ESPECIALLY OF THE NUCLEAR TYPE PREFERABLY WITH ELECTRONIC REHEAT CONTROL AND AN ELECTRONIC REHEATER I [75] Inventors: Michael C. Luongo, Brookhaven;

James A. Martin, Jr., Newtown Square; Donald N. Tapper, Media,

I all of Pa. [73] Assignee: Westinghouse Electric Corporation,

' Pittsburgh, Pa.

[22] Filed: Mar. 9, 1972 21 App]. No.: 233,076

t.. L 2 l ;Ql E.LILILL' '..f 'L' 13.11 If: .t

[51] Int. Cl. Folk 7/16 [58] Field of Search 60/70, 73, 105

[56] References Cited UNITED STATES PATENTS 3,097,490 7/1963 Callan et al 60/105 MANUAL INPUT SOURCE i' COMPUTER- ACTUNOR i} CONTROLLER [111 3,792,583 [451 Feb. 19, 1974 3,511,051 5/1970 Mitchell 3,552,872 l/l971 Giras et al. 235/151 X 3,561,216 2/1971 Moore, Jr. 60/73 3,630,839 12/1971 Podolsky 60/73 X Primary Examiner--Martin P. Schwadron Assistant Examiner-11. Burks, Sr. Attorney, Agent, or FirmE. F. Possessky ABSTRACT within predetermined constraints and according to predetermined functions of time.

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1 ELECTRIC-POWER PLANT SYSTEM AND METHOD FOR OPERATING A STEAM TURBINE ESPECIALLY OF THE NUCLEAR TYPE PREFERABLY WITH ELECTRONIC REHEAT- CONTROL AND AN ELECTRONIC REHEATER CROSS REFERENCE TO RELATED APPLICATIONS 221,185 filed Jan. 27, 1972- entitled Electric Power Plant System and Method for Operating a' Steam Turbine Especiallyof the Nuclear Type with Electronic Reheat Control of a Cycle Steam Reheater by M. C. Luongo et al.

BACKGROUND OF THE INVENTION This invention lies in the fieldof electric power plants and, more particularly, automatic control systems for continuously and automatically controlling the steam reheating operation in a nuclear turbine system.

A characteristic of nuclear steam generators, utilized in the production of electric power, is that, the steam produced therefrom is of a generally lower temperature than that of steam generators powered by non-nuclear or fossil fuel sources, such that, the generated steam is substantially at a saturation temperature containing not much more energy than that required to evaporate water. Consequently, as soon as a relatively small amount of energy is taken out of the steam, by the developments of turbine drive in a high pressure turbine section, moisture forms in it which would otherwise make the steam unusable for further driving of the turbine. For example, in nuclear turbine operation the steam being exhausted from the high pressure turbine section enters the saturated (wet) condition at approximately 35 percent of rated turbine load, due to the energy which is being taken out of the steam. Yet, the same steam is needed for use in developing turbine drive in one or more lower pressure sections of the turbine system. Further, it is extremely important to prevent excessive temperature of the lower pressure steam, as well as, conditions of rapidly heating cold turbine parts as in the case of a cold start, overheating and overstressing of low pressure turbine exhaust parts, as in the case of low load operation, and rapid cooling of the lower pressure turbine section (hereinafter referred to as the low pressure turbine section) in the case of a hot start. In one specific turbine system design, the maximum instantaneous temperature change of the steam to the LP turbine inlet must be limited to 100F, due to thermal stress and possible distortions of the low pressure (LP) turbine stationary parts. Except for such an instantaneous steam temperature change, the rate of change of this temperature must not exceed 250F per hour, in order to avoid excessive distortion or fatigue cracking Of the turbine parts.

Generally, in nuclear power plants, the steam reheat function is normally performed outside the primary steam generator, as opposed to the case of fossil plants where reheat is typically performed inside the primary steam generator. Since the nuclear reheater steam temperature maybe considerably different from the LP section inlet steam temperature, both the difference between the two steam temperatures and the rate at which that difference changes may require control, since large temperature differences can cause excessive low pressure turbine section stresses.

Although varying systems specifications are possible,

a typical control specification for starting a nuclear turbine system provides that no reheat-system is to be passed through the reheater until the plant has been brought up to 35 percent of full load as measured in terms of pressure or electric power delivered (megawatts). Such a control specification is designed to decrease the temperature differential between the reheat steam temperature and the low pressure section inlet to about 100, before beginning the opening of the reheater control valve which determines the flow of re heat steam. Under these. conditions experience has shown that a suitable rate of reheater valve opening provides for a gradual increase in opening from O to 100 percent over a period of one hour.

Once the system has been brought to a full reheat steam mode of operation, it may be maintained there as long as the actual load remains above 10 percent of full load. This operating condition has been found to be permissible because the temperature differential, under such conditions between the reheat steam and the low pressure section inlet temperature, is not sufficiently great to causeexcessive turbine stresses. If the load should drop to'below 10 percent of full load or less, it becomes necessary to reduce the steam temperature at the low pressure section inlet, particularly to protect against overheating of the last row of rotating blades of the low pressure section.

During low load conditions (10 percent or less of full load), there is a very low flow of cycle or motive steam. The last row of blades in a low-pressure turbine section do not work, that is, there is substantially no expansion of steam through these blades, and they act more or less as compressors or pumps and simply windmill around in a steam atmosphere. As a consequence, these blades start to heat up considerably, causing another condition where these blades may be overheated. Accordingly, a typical specification for a nuclear steam turbine system includes the provision that the inlet steam temperature at the low pressure section must be brought down below a low load limit (such as 400F) within 15 minutes of the first occurrence of a load drop 7 below the 10 percent of full-load level.

ing the startup process. This type of operation is referred toas "hot start and the control in this case must permit the rapid opening of the reheater steam valve in order to avoid excessive cooling of the turbine parts. Summarizing then, the three basic temperature controls which are necessary in a nuclear steam turbine system or any system where a separate heat transfer unit is utilized for reheating are: (l) reheat steam temperature rate of increase control during cold start to regulate the absolute value of the steam and structural temperature at the low pressure section inlet and the rate at which these absolute values are permitted to change; (2) temperature regulation of the inlet temperature and low pressure turbine end temperature below a maximum temperature unit during low load operation; (3) a hot start mode of operation where it is necessary to prevent excessive cooling of the low pressure turbine.

In addition to the above specification, certain other control specifications must be met in a system of the type described above. These specifications may be summarized as follows: l provision must be made to protect the system from excessive absolute reheat temperature at the inlet of the low pressure section in the order, for example, of 540 or higher; (2) provision must be made to permit the resetting of the reheat steam flow control to permit, for. example, a new cold start operation; and (3) provision must be made to per mit a human operator to override the automatic control apparatus.

To enable downstream motive use of the wet stream, it is standard practice in designing nuclear turbine systems to incorporate separate moisture separatorreheater apparatus to control the moisture content of the steam which is cycled from the high pressure turbine section to the low pressure turbine section. One example of said apparatus is disclosed in copending application Ser. No. 763,885 now US. Pat. No. 3,574,303 assigned to the present assignee, entitled Moisture Separator Reheater for Pressurized Vapor and filed by T. J. Rabis on Sept. 30, 1968.

A reheater control valve is normally used to regulate the amount and rate of steam temperature increase of the turbine cycle steam passing through the reheater. The regulation of such cycle steam may be accomplished by opening and closing the reheater control valve, thus controlling the amount of heating steam passing, through the reheater tubes, and accordingly the amount of heat which is transferred to the turbine cycle steam, temperature is increased, and vice versa.

A commercially supplied prior art turbine control scheme is shown and described more specifically in a printed paper entitled Electrohydraulic Control for Improved Availability and Operation of Large Steam Turbines" presented by M. Birnbaum and E. G. Noyes to the ASME-IEEE National Power Conference at Albany, New York during Sept. 19-23, 1965. In that scheme, feedback control is employed to regulate turbine speed and load-in large electric utility steam turbines. Some digital circuitry is included, especially a solid state digital reference system which eliminated earlier speed/load changer motor systems, for establishing the turbine speed and load setpoint changes on a permissive ramp scheduled basis. An article entitled Automatic Electronic Control of Steam Turbines According to a Fixed Programme in the Mar. 1964 issue of the Brown Bov eri Review relates to similar subject matter.

Another prior art apparatus is described in Eggenberger et al., U.S. Pat. No. 3,098,176, issued July 16, 1963, entitled Electric Long Range Speed Governor" and in Eggenberger et al., US. Pat. No. 3,097,488, issued July I6, 1963 entitled Turbine Control System.

In the prior art, reheater control apparatus typically has consisted of a motor-operated cam, adapted to send an error signal to a pneumatically operated control valve. However, such a system has been commercially unattractive because of size and bulkiness, incompatibility with other forms of equipment, and particularly because it requires excessive, operating time.

More particularly, one type of prior art control has been referred to as a time-pattern transmitter and operates through the use of a motor-operated cam which in turn controls the transmission of an air signal to a reheater control valve. The so-called time-pattern transmitter is not fully automatic and still requires a considerable amount of the operators time to insure that the various modes, which have been specified, are being properly executed. Although the cam control of air transmission is satisfactory at the turbine site it may not be permitted in some plants in the control room. Thus, the prior art system may not be conveniently interfaced by remote control with a turbine control system.

Another limitation of the referenced prior art approach has been the lack of automatic regulation control through the use of any feedback. This means that the operator has been required to adjust a cam in the case of low load control where it may be necessary to regulate to a temperature range in the region of 400F. A further disability of the prior art system has been that the motor-operated cam system or time-pattern transmitter does not have logically set modes which may be established remotely or otherwise by means of a programmed computer system or other automatic controller. This means that it has not been feasible in a practical sense to automatically switch from one mode to another through the use of the prior art. Thus, there has been a need in the electric power industry for a nuclear turbine operated by a control system which is capable of being miniaturized and mounted at any desired remote location, which is reliable and inexpensive, which can be efficiently tied into computer operation, which provides performance improvement in the steam reheat function, and which requires a minimum amount of operator time.

There is provided a method and apparatus for operating an electric power plant, and nuclear type turbines therein, with controlled steam reheating preferably according to a selected one of a plurality of modes of control operation. The apparatus preferably controls reheat steam conditions to provide variously for controlled linear increase of low pressure turbine temperature from a first LP turbine temperature to a second LP turbine temperature upon cold turbine start; controlled operation at a predetermined LP turbine temperature at low plant load; fast rise time increase LP turbine temperature to a predetermined LP turbine temperature; and manual takeover by an operator. A mode control switching circuit functions with a computer or other means to enable operator selection of the desired mode of control. The system is automatically reset to a minimum LP turbine operating temperature when it is first turned on, and is automatically placed in a temperature limiting mode of control, to the exclusion of all other modes except the manualmode, when the sensed LP turbine operating temperature exceeds a predetermined value. In the preferred embodiment, the sensed LP turbine temperature is that of stationary LP turbine structure near the LP inlet.

P throttle pressure Kp constant of proportionality S steam flow K constant of proportionality. When the throttle pressure is held substantially constant by external control as inthe present case, the turbine load is thus proportional to the first stage impulse pressure P,. The ratio P,/P may be used for control heater valve transducer which in turn activates the re-- heater valves and accordingly controls the reheating applied to. the steam being cycled from the high pressure turbine section to the low pressure turbine section(s). The inlet steam temperature(s), of the low pressure turbine section(s), is sensed and compared with a high temperature limit signal. The system is automatically placed in a temperature limit control mode when the low pressure inlet steam temperature or the hottest of such values is sensed and has a temperature exceeding the high temperature limit.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 shows a block diagram of an electric power plant including a nuclear. turbine system operated in accordance with the principles of this invention; FIG. 2 shows a block diagram of an electronic control system operable with the nuclear power plant and turbine system shown in FIG. 1 and in accordance with the principles of this invention;

FIG. 3 shows a detailed circuit diagram of the control system shown in FIG. 2;

FIG. 4 shows a graph of an ideal variation of low pressure inlet steam temperature with time as produced in response to placing the control system in the cold start mode;

FlG. 5 shows a curve-representing the'relationship between areh'eater control-signal and the temperature of the reheated steam; and

FIG. 6 shows a schematic diagram of a mode control unit employed in the control system.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIG. 1, the overall system of this invention is shown in block diagram form. A nuclear reactor 16, a pump 17, and a nuclear steam generator 18 are illustrated as located within a containment shell or vessel 19. By means well understood in the electric power plant art, the combination 16, 17, 18 provides for a transformer of nuclear energy to steam energy, with the output of the nuclear steam generator 18 being a source of steam suitable for driving a nuclear turbine-generator system. Since the reactor 16 in this case is in the form of a pressurized water reactor, the steam output is generated in a secondary loop by heat transfer from the reactor coolant which flows in a primary loop. In other applications of the invention, the apparatus configurations employed to generate steam may vary, as would be'the case, for example, if a boiling water reactor were employed.

As used in this disclosure, the term nuclear turbine refers to a turbine system driven by steam derived from the energy of a nuclear reactor. It is, of course, to be understood that any turbine system powered by relatively wet stream, from whatever source, would possess similar inherent characteristics to be classifiable as a nuclear type turbine, and accordingly, although the invention is especially adapted for and is especially useful with nuclear turbines in nuclear electric power plants, it can have applications in non-nuclear installations where nuclear type turbines are employed.

The hot main stream is carried from containment vessel 19 by main steam piping 21, to distribution point 39. From point 39, the steam is carried through parallel paths. A first of such paths carries the heating steam through the reheater valves, RVl-RVN. The other illustrated paths each carry the steam through a throttle valve TV and governor valve GV, to a high pressure (HP) turbine section 30. The TV and GV valves may be actuated 'andcontrolled either manually from a computer controller unit 700, or as preferred in the present instance, from a conventional electronic analog electrohydraulic valve position control system 702.

The throttle and governor valves are operated to control the turbine speed during startup and the turbine load and frequency participation during synchronous operation. Such control can be implemented with conventional control loop arrangement. One example of prior art control suitable for the control 702 is that set forth in US. Pat. Nos. 3,097,488 and 3,098,176 A speed transducer 704 is coupled to a-rotor, shaft 32 thereby generating a signal which is proportional to the speed of turbine sections 22 and 30.- The signal from the speed transducer 704 is fed into the analog system 702 and is utilized thereby for determining throttle value (TV) and governor valve (GV) position. In the course of passing through the HP turbine section 30, the steam releases much of its energy to the turbine, and becomes relatively heavily laden with moisture. The steam from HP section 30 exits through a plurality of HP exhaust outlets, only one of which is shown in FIG. 1 (at 31).

The HP turbine element 30 is coupled through a rotor sahft 32 to a plurality of low pressure (LP) turbine sections 22. As indicated diagrammatically in FIG. 1, there may be any number of such low pressure sections coupled in tandem to drive the common shaft 32. Each LP turbine in the system is suitably a double flow turbine, and is thus considered to have two sections, or

elements. As used in this specification, LP turbine section is defined to mean a lowpressur'e turbine component receiving input steam downstream from the moisture-separator and reheater, and providing output power. The outputpower from all of the LP turbine sections, as well as that provided by the HP turbine section, is coupled through the shaft 32 to a conventional electric generator 12, which converts the rotational energy ofthe shaft to electrical energy. A breaker system 15 and a load 17 are connected to the generator 12. Thus, the entire system provides successive. energy transformation from the nuclearfission energy in the reactor 16, to heat thesteam in the steam generator 18, to kinetic energy at the turbines, and thence to electrical energy at the generator 12. The basic apparatus so far described forms a generally well known nuclear electric power plant and steam turbine installation which requires no further description on structural detail for a skilled artisan s understanding of the invention and the manner in which the invention can be embodied with such apparatus.

A megawatt (MW) transducer 706 connected to an output of the generator 12 generates an output signal which is fed to the analog control 702 where the signal is utilized to determine CV and TV value positions.

The moisture laden steam exhausted from exhaust outlet 31 of the HP turbine section must be recondienthalpy toa supreheated level. Suitably, the system contains an independent reheater path from the HP turbine section to each of the LP turbine sections. Only one such path is shown in detail in FIG. 1, for clarity of illustration. However, as indicated, each LP turbine section may be fed from the HP turbine through a separate moisture separator and reheater path. Accord-V ingly, the subsequent discussion of the reheater control system is directed to a single reheater stream flow path with the understanding that similar comments apply to the reheater path for eachLP section.

At point 39, main turbine supply steam is diverted through a reheater valve RV, which is a suitable pneumatic-actuated valve which controllably allows passage of the main steam. The valve RV is preceded by a shut off valve 50, which canbe operated to prevent passage of the main steam through to the reheater, and shunted by a conventional purge valve PV. Valve RV is actuated by a reheater valve actuator 50, which is a conventional electropneumatic transducer, designed to convert an electrical input signal into a pneumatic output signal. Actuator 50 is supplied from a regulated air pressure source (not shown) and produces an electrically controlled pneumatic output which is coupled to and causes the positioning of all reheater valves RVlRVN, which in turn determine the amount of heating steam which passes to the reheater. The actuator 50 is controlled electrically from a master ocntrol system 90, the details of which are described hereinbelow.

The controlled steam flow through valve RV, comprising relatively dry heating steam derived from the main steam source, ispassed through a reheater 40. The reheater 40 is a conventional unit well known in the art, functionally adapted to transfer heat from the heating steam passing through reheater valve RV to the cycle steam which has been exhausted from the HP turbine. The reheater 40 maybe single stage or double stage. The single stage reheater, as illustrated, typically receives its heating steam from the main stream line ahead of the turbine inlet throttle valve. On typical units with two stage reheat, the first stage reheater utilizes steam from a highest pressure HP turbine extraction point while the second stage reheat steam source is from the main steam lines ahead of the HP turbine inlet, as atpoint 39 in FIG. I.' t

The heating steam, which passes through the reheater, gives up energy to raise the enthalpy of the turbine cycle steam and the heating steam becomes relatively wet and is passed out of the reheater as condensed water. With reference now to the cycle steam, water is drawn out of it by the moisture separator 35. The water thus drawn out of both the reheater 40 and the moisture separator 35 is piped back to a feed water heater system 37 wherein it is heated to a temperature suitable for reentry into the steam generator 18.

The superheated-dry cycle steam, which flows to the LP turbine sections from the reheater 40 at LP inlets, gives up energy to meet turbine load ultimately emerges from the LP exhaust outlets. The exhaust steam is collected from each LP turbine section and passed through a condenser 70, the output water of which is passed through the pump 38' and thence to the feed water heater system 37. I"

. With continued reference toFIG. 1, there is shown, diagrammatically a series of temperature detectors -1 through 80-N corresponding to the plurality of LP turbine sections in the system. The temperature detectors are suitable thermocouples, or otherequivalent temperature sensing devices,and are suitably mounted at each LP steam inlet, preferably to sense the metal temperature of stationary turbine structure at that point as caused by the reheated steam which is being introduced there. Each thermocouple (temperature) signal is connected through a transmission line (labeled T/C) to the control system 90, the plurality of T/C signals constituting feedback inputs to the control system, as well as representations of the turbine temperature variables which are ultimately controlled torestrict the amount of turbine metal thermal stress and generally to provide improved turbine power plant operation. ,As discussed hereinbelow, the control system generates control signals which are .connected to the actuators 50, thus controlling thedegree of cycle steam reheating, and thus thetemperature and other intermediately' variable conditions of the steam entering the LP sections. More particularly, the conditionsof the cycle flow steam, at the LP inlets are affected by, l system operating determinants including cycle steam flow control applied by the controls 25 and the valves GV and TV at the HP inlet, the HP inlet steam throttle pressure and temperature andthe operating load on the turbine system and 2) the operation of the moisture separator 35 and the reheater 40. As system operating determinants change with system operation to cause or tend to cause changes in the LP inlet steam conditions and the LP inlet metal structure temperature, corresponding changes are made in the reheater operation to cause the controlled LP inlet conditions to behave in the desired manner. Of course, some of the system operating determinants such as the steam throttle pressure and temperature are themselves independently controlled and such control accordingly affects the conditions of the cycle steam at'the LP inlets. For example, a drop in thetemperature of throttle steam can decrease the reheat capability. It is also noteworthy that the system operating determinants, such as the steam throttle pressure and temperature, have some effect on the heating capability of the heating steam in thereheater for any given position of the reheater valve. The T/C signals reflect what is happening to the steam temperature and to some indirect degree what is happening to other steam conditions at theLP inlets, and accordingly the T/C signals ultimately reflect the net impact of all interacting variables on the LP inlet steam conditions.

Also, indicated diagrammatically, in FIG. 1, is a mode control unit 95. The unit provides operator determination of the particular mode of the plurality of automatic modes of control provided by the control system 90. The mode control may be computer controlled through the computer-controller 700, or it may be manually controlled through a pushbutton control panel. In the event that an operator desires to take over complete control of the system, as opposed to placing it in any one of the various available modes, an operator setting unit 650 is also provided.

As illustrated in FIG. I, there are six modes of control preferably .available in a system operated in accordance with this invention, and these modes can be set manually at any time by the operator. A seventh mode, namely the temperature limit mode, is entered into automatically by the system, in response to detection of an LP inlet temperature in excess of a predetermined temperature limit. When placed in this mode, the operator cannot put the system into any other mode of control except manual until the highest LP inlet temperature has decreased to a second and lower predetermined limit. The preferred modes of control provide for improved plant, turbine and reheater operation and they are summarized in the following table:

TABLE I CS (cold start) In the CS mode, the lift of the reheater control valves is controlled over a fixed period of time according to a programmed curve for cold turbine startups. In the preferred embodiment, the turbine inlets are raised linearly in temperature from 300F to 500F over a period of one hour.

T (maintain 400F) In the T mode, the reheater control valves are automatically positioned so as to maintain the temperature at thehottest LP turbine inlet at 400F after load reductions to percent, or below, of rated output power, which reductions are to be held for periods exceeding minutes. This control prevents the possibility of overheating the last two rotating rows of blades of the LP turbine section.

H (hot start) In the H mode, the reheater control valves are opened quickly to a point equivalent to an LP inlet temperature of 400F, for hot turbine startups. R (reset) In the reset mode, the reheater steam control valves are closed, ensuring a cold temperature at the LP inlets. The system is placed in reset after the turbine has been shut down for some length of time, and prior to a cold re-start.

M (manual) When in this mode, the reheater control valve positions can be controlled manually by an operator.

CP (computer) When in the CP mode, the overall system is under the control of a computer-controller. In accordance with real time computer calculations, the computer actuates the control system into either the CS, T, H, or R, mode. The system may be placed into and taken out of the CP mode at any time by the operator.

TL (temperature limit) The control system is placed into the TL mode automatically, in order to maintain an absolute high temperature limit to protect the LP turbines. When in the TL mode, all other modes are locked out, except manual, manual being the only mode into which the operator can then place the system. The control system automatically returns to the CS mode of operation after the hottest turbine temperature has been detected to'have dropped by a predetermined amount. I

It is understood that the systemoperator can change from one mode to another mode at his discretion (unless the temperature limit is exceeded). For example, if, while in the T mode, load is increased, the system may be placed in the CS mode at 35 percent load. The reheater valves will then open and increase the temperature of the LP inlet steam from 400F to 500F at a uniform rate.

With reference now to FIG. 2, the preferred elements of the control system are shown in block diagram form. The thermocouple inputs, designated T/Cl through T/C-N, are shown connected to respective thermocouple amplifiers, designated as TCA1 through TCA-N. Each thermocouple amplifier is a stable high gain proportional amplifier, utilizing an operational amplifier within an open loop gain on the order of 10 Further, each thermocouple amplifier has differential inputs, with a second input connected to a thermocouple cold junction compensation unit which provides a controlled voltage level which isadapted to represent the voltage output of a cold thermocouple. Thus,,the output of each thermocouple amplifier represents the increase in temperature, as sensed in itsrespective LP turbine section, over the cold state. In practice, the outputs of the thermocouple amplifiers are coupled to temperature indicators mounted on the main panel, which provide a visual representation of the temperature at each LP inlet.

The output of a conventional auctioneering or CTC circuit represents the highest LP inlet temperature and it is processed by the control system 90 in either the H or T mode. In both the H and T modes, the reheater control valves are to be opened eventually to a position which provides heating steam flow resulting in an LP inlet temperature of 400F at the hottest LPinlet.

' The auctioneered temperature signal is connected to one of two inputs of the comparator 100. The other input circuit of the comparator is normally connected to a low temperature reference L, which reference provides a reference voltage equivalent to an LP temperature of 400F. The comparator 100 is a unity gain circuit which compares the auctioneered temperature input with the 400F reference input, and produces an output signal which is positive or negative depending upon whether the sensed highest temperature is higher or lower than. 400F respectively. The output magnitude of the comparator 100 is proportional to the difference between the LP temperature signal and the temperature reference signal, and is thus a classic error signal as generated in feedback systems. It is to be noted, of course, that the temperature reference ll0L may be adjusted to correspond to any other desired LP inlet temperature.

The output of the comparator 100 is coupled through a switch HX to either a low load rate control element 250L, or a hot start rate control element 250B. The element 250L is a large resistor, nominally of the order of 2 megohms, and is connected into the control circuit for operation in the T, or 400F mode. The element 250l-I is a relatively small resistor, and is switched into the circuit corresponding to the mode H, or the hot start mode. The outputs of both 250L and 250H are connected to one of two input terminals of a two position switch KZX, which switchably connects the one input terminal to a ramp generator 350.

A cold start rate control circuit 300 provides a reference voltage which, when connected to the ramp generator 350 and a function generator 400 through the other input terminal of the switch K2X, causes operation of the reheater valves to operate so as to produce the LP inlet temperature change shown in FIG. 4. In the cold start mode, the desired characteristic is a linear rise of temperature from 300F to 500F, which takes place over a period of one hour. The signal provided by the circuit 300, when operated upon by the characteristics of the ramp generator 350, a function generator 400, and a power amplifier 500, causes the generation of an electrical output signal which produces an optimum approximation of the ideal LP inlet temperature versus time response shown in FIG. 4.

The temperature versus time generator, or ramp generator 350, is an operational amplifier connected in a well known manner to provide the mathematical function of an integrator. The slope of the output of generator 350, representing voltage versus time, is of course a function of the magnitude of the input'signals, and thus varies depending upon the mode in which the control system is placed. The range of the ramp output suitably extends from volts to about 10.5 volts. A reset circuit 380, operated by a reset switch RX, provides the capability for clamping the output level of the generator 350 to a predetermined minimum level, so as to place the reheater valves in a substantially closed position when in the reset mode.

It is noted that the positive voltage of the reference circuit 300 is designed to provide a linearly increasing ramp output, so as to provide a linear rise from 300F to 500F over the specified time interval. Additionally, a negative reference voltage, not shown, but of the same magnitude, may be switchably provided, such that, when connected to the input of the generator 350, the generator output is reduced linearly, as from -l0 volts to 0 volts. This reference would be used, for example, in the situation where the low pressure turbine temperature was at 500F and it was desired to reduce it linearly to 300F. It is noted that, in this situation, a conventional diode clamp circuit (not shown) is provided at the output of the ramp generator 350, to clamp the output at 0 volts and prevent the output from going to a positive value.

A function generator 400 comprises a diode-resistor logic network, which acts operationally as the input circuit of the power amplifier 500, and thereby controls the output of the amplifier 500 as a characterizing function of the output of the ramp generator 350. As is well understood in the art, the reheater valve actuator 50, which is an electropneumatic device, would ideally have a linear electrical/pneumatic characteristic. Similarly, the reheater valves themselves would ideally pass an amount of heating steam directly proportional to the valve lift. However, in practice, the overall char acteristic of the reheater valve lift versus LP inlet temperature 1 is non-linear, and is approximated by a straight line segment curve shown in FIG. 5. It is this approximation of the reheater characteristic which is achieved in a well known manner by the function generator 400.

The power amplifier 500 amplifies the output of the function generator 400 to a level sufficiently high to drive the reheater valve actuator 50. Coupled to the input of the amplifier 500 is a zero ofiset circuit 550,, which holds the input to the amplifier at a minimum and which yields an output of +1.0 volts with a zero ramp input, thereby satisfying live zero requirements of the reheater valves. At an output of +1.0 volts, the reheater valves are in a fully closed position. It is to be remembered that in the present embodiment the actuator 50 drives each of the several reheater valves, such that the feedback control signal from the power amplifier 500 controls the inlet steam temperature of all the LP turbine sections. The maximum output of the power amplifer 500 is suitably clamped, by a conventional diode clamping circuit, not shown, at approximately +9.5 volts.

When the system is placed in the manual mode, the switch MX connects the reheater valve actuator 50 directly to the conventional operator setting circuit 650. The operator may thereby manually control the signal to the actuator 50, and control the entire reheater systern and the power plant as it is affected by the reheater operations.

With further reference to FIG. 2, the reference input to the comparator is switchably connected to a high temperature reference No. l, designated TL, which supplies a voltage reference corresponding to an LP inlet temperature of typically 540F. The auctioneered LP temperature signal is also coupled into the comparator 200, which comparator has a second input connected to a high temperature reference No. 2 (210), which is a voltage, source corresponding to a predetermined high temperature limit, typically 550F. When the auctioneered temperature signal exceeds the voltage of reference No. 2, corresponding to the situation where the hottest LP inlet temperature signal is in excess of the high temperature reference No. 2 signal, an output signal is derived from the comparator 200 which drives a relay drive 220, which in turn drives a relay KIR. The relay KIR causes a switch KlX to close, which in turn causes the energization of temperature limit relay TLR, which causes switching of a switch TLX. Thus, when the high temperature limit (reference No. 2) is exceeded, the input to the comparator 110 is switched from a low load temperature reference 110L to the high temperature reference No. l.The high temperature reference No. 1 is normally set at 10F below high temperature reference No. 2, such that, as soon as TLR is energized, the output of the comparator 100 becomes negative, causing the ramp generator to decrease in output, thereby tending to close the reheater control valves.

It is to be noted that the above-designated temperature references are arbitrary in level, and may be chosen to adapt to the particular system to which this invention is applied. The temperature references used herein are for illustrative purposes only, and the temperature differential between high temperature reference No. l and No. 2 may similarly be adapted to the specific system parameters. Comparator 200 has an off-on differential, suitably about 20-30F, such that an output from the comparator 200 is maintained until the auctioneered LP inlet temperature has dropped to 2030F below thehigh temperature reference No. 2. Until this happens, the system is maintained in the TL mode, thus holding the hottest LP inlet at 10F below hightemperature reference No. 2 until the operator does something externally to cool off the LP turbines.

With reference now to FIG. 3, the circuit specifics of the preferred control system 90 are explained in more detail. The circuit temperature control CTC comprises a diode-resistor combination, the diode CTC-D being chosen for its temperature-voltage characteristics,

which are such to substantially cancel out any signal variations caused by changes in the preceding circuitry. Resistors R96 and R97 are chosen to cooperate with the characteristics of the diodes CTC-D, andare suitably on the order of 3K each. i

The comparator 100 comprises an operational amplifier A101, having an input resistor R101, and being shunted by a resistor-diode network comprising R102, R103, D101, D102, D103, and D104. The shunting feedback network, with each of the diodes connected at T105 through R103 to ground, causes the polarity of an output of an amplifier A101 to depend upon whether the positive auctioneered temperature signal from the CTC circuit, or the negative temperature reference signal from the circuit 110, is greater in magnitude.

The reference circuit 110 comprises a negative voltage source, which is connected to ground through a resistor 110L, a pot P111, and a variable resistor 110TL. The variable resistor 110TL isshunted by a normally closed switch TLX', such that, the, reference voltage is normally derived solely from'the negative source, the resistor 110L and the pot 111 (suitably 2,000 ohms) providing a reference voltage corresponding to a temperature reference of about 400F. When the switch TLX' is opened which correspondsto the detection of a temperature limit, the variable resistor 110TL is placed in series with the reference circuit, thereby raising the voltage sensed at the pot 111, and placing a higher temperature reference signal in connection with the input of an amplifier A101.

The comparator 200, having its input connected through R204 (suitably 499K) to the output of the compensating circuit CTC, comprises an operation amplifier A201 shunted by a resistor R202 (suitably 4.99 megohms) and capacitor C203 (suitably 0.0005 uf). Also connected to the input of A201 is a negative voltage reference (550F) obtained from a pot P211 (suit ably 2,000 ohms), a variable terminal of a pot P211 being connected to an input of A201 through R212 (suitably 4.99 megohms). Thus, the input to the amplifier A201 is the sum of theLP inlet temperature signal and the 550F reference signal. vAs long as the input signal is of a value corresponding to a temperature below 550F, the output of the circuit 200 is positive. :T his positive signal is coupled to a transistor TR200 or relay driver 220, holding it in an off-biased condition. However, as soon as the LP inlet temperature signalrises to a value representing a temperature greater than 550F the output of the comparator 200 goes negative, turning on the transistor TR220. The collector of TR220 is coupled through a resistor R225 (75 ohms) to the relay KIR which has its other terminal connected to a negative voltage source. The relay KIR is shunted by an arc suppression diodeDKl. Thus, when the transistor 220 is biased on, the series circuit between the negative supply and ground is closed,- whereby the relay KIR is energized-and the switch KIX is closed (see FIG. 6). The closing of the switch KIX places a voltage directly across the temperature limit relay TLR, thus energizing it and opening the normally closed swith TLX'. Simultaneously with the energization of the relay TLR, a high temperature light TLL, in parallel with the relay TLR (see FIG. 6) is lighted, informing the operator of the condition of the system. As stated hereinabove, the relay KIR will'remain energized, keeping the system in the TL' mode, until the operator takes action to manually reduce the temperature of the hottest LP inlet, or until for any other reason such inlet drops to a temperature approximately 2030F below the 550F reference point.

With further reference to FIG. 3, the rate control circuit 250 comprises parallel branches, the lower branch 250L having a high resistance (suitably 2 megohms), and the upper branch having a relatively low resistance (suitably 100K). As is well known in the pertaining art, the gain characteristic of an operation amplifier, connected. to integrate the input signal, carries a proportionally constant K which is inverse to the input resistor. Thus, the two meg resistor designated 250L corresponds to a 10 minute rate, and is used in the T (400F) ramp generator accordingly, and causing the LP inlet temperature to attain approximately 400Fin about 30 seconds. It is, of course, noted that the switch K2X must be closed by the mode control 95 to couple either the 2501-1 or 250L resistor to the ramp generator 350.

The cold start rate control circuit 300 comprises a positive reference voltage which is connected to ground through a resistor R301 (suitably 2,430 ohms) in series witha pot P302 (suitably ohms). The output from the pot P302 iscoupled through a resistor R303 (suitably 10 megohms) to one terminal of the switch K2X. When in the CS mode, the switch K2X is positioned as shown in FIG. 3, coupling a positive voltage through to the ramp generator 350, The positive voltage continuously applied to the ramp generator 350 causes the generation of .a negative-going rampoutput from the generator 350, from substantially 0 volts to l0 volts. This negative-going ramp corresponds in valueto that desired to raise the LP inlet temperature from 300F to 500F in about one hour. By changing the value of the resistor R303, the ramp time can be changed as desired. The ramp generator 350 is a contional to R, (feedback resistor) over R the input resis-- tance, with R here being established by the dioderesistor network. Also connected to an input of the amplifier A501is a zero offset .circuit 550, comprising a negative voltage connected through a pot P551 (5,000 ohms) and a resistor R552 megohms). Thus, when the output of the ramp generator is below a given minimum, the zero offset circuit provides a minimum negative signal at the input ofthe amplifir A501. This minimum signal corresponds to point one on the straight line graph of FIG. 5, and establishes a live zero signal which is required by the reheatervalve actuator 50.

Referring to both FIGS. 4 and 5, the desired variation I of reheated steam temperature with time is shown in FIG. 4. However, the relationship between the control signal applied to actuator 50, and the temperature of the turbine cycle steam after being heated in the reheater, is not a linear relationship, but is approximately by the straight line segments of a curve shown in FIG. 5. Thus, in order to obtain the approximately linear response as shown in FIG. 4, it is necessary that the output of the ramp. generator 350 be modified, so that, corresponding to a continuously rising ramp signal, the control signal hasthe straight line segment form of the curve of FIG. 5. This is accomplished by the function generator 400.

Comparing the function generator circuitry as shown in a block 400 with the'straight line segment graph of FIG. 5, it is seen that break points 2 and 3 may be positioned by the setting of pots P402 and P403 respectively. The pot P402 is connected through a resistor R404 to a positive voltage source, and the wiper of the pot P402 is connected through a resistor R406 to a terminal point T402. The terminal point T402 is connected respectively to the cathode of a diode D402, and to a resistor R402 which buffers the point T402 from the input to the function generator. Thus, the voltage at the point T402, determined by the setting of the pot P402, is normally held positive with respect to the anode of the diode D402, which is coupled to the zero offset circuit 550. Under these circumstances, the diode D402 is back biased until the output of the ramp generator 350 becomes sufficiently negative to cause the point T402 to be negative with respect to the anode of the diode D402, thereby turningit on. At that time, the input resistance to the operational amplifier A501 becomes appreciably resistor R402 in'parallel with resistor R401, thus increasing the gain of the amplifier, as reflected by the increased slope between the break points 2 and 3. In a similar fashion, the wiper of a pot 403 is tied through a resistor R405 to a terminal T403. The terminal T403 is connected through a resistor R403 to the input of the function generator, and to the cathode of a diode D403. The anode of the diode D403 is connected to the anode of the diode D402 and to the input of the operational amplifier A501. The setting of the pot P403 is chosen, so that, the output of the generator 350 must increase to a greater negative voltage before the diode D403 is forward biased. This occurs at a break point 3, at which point, a resistor R403 is effectively shunted across the resistors R401 and R402, further decreasing the input resistance to the amplifier A501, and resulting in the increased slope as indicated between a break point 4 and the point 3. The point 4 corresponds to the point where the output of the ramp generator has risen to l0 volts, and at which the magnitude of the signal transmitted to reheater valve actuator 50 causes substantially a 100 percent valve lift, resulting in maximum flow of steam through the reheater valves to the reheaters. The power amplifier 500 comprises the operational amplifier A503, the output of which is fed through an emitter follower (comprises TR500, R502 and R503) to derive a control signal suitable for transmission to the actuator unit 50. The output of the emitter follower is switchably connected through the switch MX to the actuator 50. When the switch MX is closed, corresponding to manual operation, the operator can adjust a potentiometer P642 (250 ohms), which is connected in series with a resistor R651 (100 ohms) between a positive voltage source and ground. By adjusting the pot P652, the operator can directly control the voltagewhich is transmitted to the valve actuator 50. Thisis done if there is a breakdown in the electronic control circuitry, or for any other reason the operator wishes to take manual control of the system.

Referring now to FIG. 6, the schematic diagram of the manual or computer operated mode by a control unit is shown. Power is provided to the control unit by closing the switch PX and transmitting regulated positive voltage to a point 952. Upon closing the switch PX, a time delay relay TDR, connected between the point 952 and ground, is energized. The relay TDR has the operating characteristic of operating after a short time delay, on the order of Sseconds, after which delay a normally closed switch TDX is caused to open. The switch TDX is connected to the point 952 through a line 951, and causes energization of a reset relay RR at the time that the switch PX is first closed. Energization of the relay RR causes the closing of a switch RX, which connects the relay RR to the point 952 through normally closed switches CPX, MX', CSX', TLX', TX and I-IX'. Consequently, when switch TDX opens after the short time delay, the reset relay RR is held energized through the switch RX, causing the system to turn on in the reset mode of operation. This is done in order to allow sufficient time for the power supply and the amplifiers to stabilize. In the absence of this provision for automatically placing the control system in the reset mode, the system could settle out in any given'mode, which could be harmful to the turbines if not quickly caught by the operator.

It is also noted that theoperator may, at any time, place the system in the reset mode by a' switching switch RB, the common terminal of which is connectedto the terminal 952 through a normally closed switch CPX. Upon switching the switch RB, power is provided to the reset relay RR, which holds itself energized after the switch RB is released to its normal position. As discussed hereinabove and as illustrated in FIG. 3, the closing of the switch RX also clamps the output of the function generator 350 substantially to zero, holding the valve control signal at the-live zero level shown in FIG. 5. f

, As'is seen in FIG. 6, each of the modes CS, T, H and M has a corresponding mode selector button, being CSB, TB, HB and MB respectively. These buttons, along with CPB and R 3, are displayed prominently on the system control panel. The buttons are shunted by corresponding switches SCX, TX, I-IX and MX respectively, which act to hold the respective mode control relays operating after the companion button has been released. With the reset button RB in its normal position as shown, power is supplied through to the point 954, and is connected, from there to each of the four control buttons, as long as the temperature limit relay TLR is not energized. If the relay TLR is energized, the switch TLX', connected to the point 954 is caused to open, such thatno power can get through to the control relays for the CS, T, and H modes. However, underthese circumstances, the operator can place the systemin manual control by pressing a button MB which is in series with the manual relay MR, which when activated closes the switch MX.

Each of the four control buttons is placed in series CSR relay and place the system in the cold start mode.

Correspondingly, the buttons TB, HB, and MB are connected between the point 954 and corresponding mode relays TR, HR, and MR through three normally closed switches in series, each of which is energized by one of the other three mode relays. By this scheme, the system is placed in only one of the four modes (CS, T, H, and M) at a time. Panel lights CSL, TL, HL, and ML shunt relays CSR, TR and MR respectively, to indicate the mode of the system.

The line 951 carries power to the point 957, which is tied through parallel paths to a point 959, and from the point 959 through the normally closed switch MX to and through the relay K2R to ground. A first parallel path, between thepoint 957 and the point 959, contains the normally open switch TLX, which is closed only when the temperature limit is exceeded. When the switch TLX is closed, and thecontrol system is not in manual mode, the relay KZR is energized, causing switching of the switch K2X which is illustrated in FIG. 2. Under these circumstances, high temperature refer ence No. l is connected through to the comparator 100, and the system is stabilized, at a high temperature (suitably 540F), until the operator manually brings it to a lower temperature. The second parallel path, between the point 957 and the point 959, comprises a normally closed switch CSX (which opens when the relay CSR is energized) in series with the parallel configuration of the switches HX and TX, both normally open. Thus, when the computer is not in the CS mode, and is placed in either the H or T mode, power is connected through to the relay KZR, causing switching of K2X (as shown in FIG; 2), whereupon the low load temperature reference llL is connected to comparator 110. g

The button CPB, the computer mode button, is connected in series with the relay CPR, between the point 953 and ground. Light CPL shunts the relay CPR, to give visual indication of when the system is in the computer control mode. Upon closing of the button CPB, the relay CPR is energized, causing switch CPX to switch and transfer power to the point 956 shown illustrated within a computer contacts unit 955. The point 956 is connected to the computer controller 700, (FIG. 1), and when it is energized, power is prevented from being connected to any of the other mode switches (due to the position of CPX), such that, only the computer has control of the system. Point 956 may be physically connected to the computer, or any terminal point which is in turn electrically connected to the computer so as to give it control.

As seen in FIG. 1, a plurality of data inputs are provided into computer controller 700, representing information monitored from throughout the system. For example, the pressure in each of the turbine sections is monitored at a specific point, and may be converted through suitable transducers into signals which are transmitted to computer controller 700. In a similar fashion, a representation of the megawatt generation of MW of generator 12 is fed into computer controller 700.

In the preferred embodiment, an analog computer is included in the computercont'roller 700. A digital computer would form another embodiment.

18 The operation of the system in each of the aforementioned control modes can now be understood, in view of the description above. When the system is placed in v the CS (cold start) mode, switch CX is closed, and power is transmitted through the switches PX, CPX, RB, TLX, TD, HP, and MB to relay CSR. With relay CSR energized, all other modes are deenergized, and the voltage reference provided by the unit 300 is connected straight through to the ramp generator 350. The meg resistor of the circuit 300, in combination with the feedback capacitor of the generator 350, combines to produce a ramp output adapted to cause valve lift over a period of about 60 minutes, carrying the LP inlets from a temperature of about 300F to 500F.

When placed in the T mode, the relay TR is energized, thus closing the switch TX and connecting the output of the comparator 100 to ramp generator 350 through the low load rate control circuit 250L. Unless or until the temperature limit (as provided by high temperature reference 210) is exceeded, the low load temperature reference 110L (400F) is connected as an input to the comparator 100 along with the auctioneered highest LP inlet temperature signal. The comparator 100 thus continuously provides an error signal by holding the highest LP inlet temperature at 400 1 25F.

In the H (hot start) mode, a switch I-IX is closed, and

the output of the comparator is connected to the ramp generator 350 through the hot start rate control circuit 250H. By switching the relatively low resistance (about 100K) of the circuit 250H into the input connected to the generator 350, the generator output builds up much quicker, i.e. in about 30 seconds. Thus, the temperature of the highest LP inlet raises to the 400F reference quickly, at which point the control is essentially the same as that of the T mode.

As set forth hereinabove, when the system is placed in the reset mode, the switch TX is closed, and the system is incapable of going into the CS, T, H, or M modes. With the switch RX closed, the output of the ramp generator is held appreciably at zero, such that the control signal which is communicated to the actua- I01 50 is provided essentially by the zero offset circuit 550, which is designed to maintain the temperature at about 300F.

In the computer (CP) mode the computer controller 700 determines the desired mode of operation. If the turbine system 14 is cold the cold start (CS) mode is selected. If the turbine system 14 is hot having been running a short time before the hot start (I-I) mode is selected. After the turbine system 14 has reached desired operating temperature the T models selected. If the turbine has been shut down a long time the reset (R) mode is utilized.

From the above description, it is seen that this invention provides an efficient means and method for carryof the overall turbine system due to more reliable temperature control.

What is claimed is:

1. An electric generating system with a control subsystem for controlling the temperature of at least some of the steam utilized in powering a steam turbine, comprising:

a steam generator providing a source of steam;

. a high pressure steam turbine section and at least one low pressure steam turbine section, operatively combined to provide a turbine output;

electrical generating means, connected to and driven by said turbine output, for generating electrical enmeans for valving a flow of steam through said steam turbine;

means for moving said valving means from one position to another;

means for sensing the magnitude of the rotational velocity of said turbine;

means connecting to said valve moving means whereby signals are transmitted from said sensing means to said valve moving means;

] means for measuring the magnitude of energy flow from said electric generating system;

means connecting said energy flow measuring means and transmitting signals to said valve moving means, whereby said valving means is moved from one position to another in response to the signals from said energy flow magnitude measuring means;

said valving means including high pressure turbine valving means having throttle-stop valving means and control valving means whereby speed and load control are accomplished during turbine startups and under load phases of operation;

reheater means for heating relatively wet steam and producing super-heated, relatively dried steam, and having a heating steam path for passing therethrough heating steam and a cycle path for passing therethrough cycle steam which is reheated by said heating steam, said heating steam path being connected to said steam source;

temperature detection means mounted relative to said low pressure section, for detecting a predetermined operating temperature of said low pressure section; and

electronic reheater control means, operatively connected between said steam source and said reheater means, to control the amount of said heating steam passing to said reheater means.

2. The system as described in claim 1 having a plurality of modes of control in each of which said heating steam is continuously controlled according to a separate function of time;

and means for maintaining said control means in a selected one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference.

3. The system as described in claim 1 comprising:

a cycle steam network, connecting said steam source to said high pressure section, connecting an exhaust outlet of said high pressure section to said reheater cycle path, and connecting the cycle steam output recycling heater means to the steam inlet of said low pressure section, so as to pass reheated and relatively dry steam to said low pressure section.

4. The system as described in claim 2, comprising at least one low pressure double flow turbine having two turbine sections, said reheater means comprising a separate reheater for reheating wet steam exhausted from said high pressure turbine before it is passed to each respective said low pressure section, cycle steam network comprising a separate path from said high pressure turbine through each such separate reheater to each respective low pressure turbine section.

5. The system as described in claim 2 wherein said reheatermeans is an element in a closed control loop including said control means, for continuously controlling the temperature at the inlet of at least one of said low pressure sections.

6. The apparatus as described in claim 3 wherein said reheater control means comprises an electropneumatic transducer for converting electrical control signals to pneumatic signals, and reheater valve means connected between said steam source and said reheater means to regulate passage of heating steam through said reheater means, said electropneumatic transducer output being connected to said reheater valve means to control the position of same, thereby controlling the amount of heating steam passing to said reheater means.

7. The apparatus as described in claim 2 wherein said mode control means is switchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operatin gparameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.

8. The apparatus as described in claim 2 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature at said low pressure inlets from a first predetermined temperature to a second predetermined temperature along a predetermined temperature path, over a predetermined time period.

9. The apparatus as described in claim 8 wherein said reheater control means has second mode signals adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.

10. The apparatus as described in claim 8 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.

11. The apparatus as described in claim 6 wherein said reheater control means comprises a reset circuit operatively connected to control said reheater valves at a predetermined lower level of reheater valve lift.

12. The apparatus as described in claim 2 wherein said reheater control means comprises manual control circuitry permitting manual control of said reheater means when said reheater control means is in a manual mode.

13. A reheater control system for a steam turbine electric generating system having at least one high pressure turbine section and at least one low pressure turbine section, a reheater system comprising:

reheater means for controlling heating steam for reheating cycle steam,

temperature detection means common for detecting turbine temperatures near steam inlets of said low pressure turbine, and generating signals representing said turbine temperatures,

21 electronic reheater control means receiving said signals from said temperature detection means and transmitting signals to said reheater means whereby said temperatures at said steam inlets of said low pressure turbine are regulated to meet predetermined criteria.

14. The system as described in claim 11 having a plurality of modes of control .in each of which said heating steam is continuously controlled according to a separate function of time;

and means for maintaining said control means in a selected one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference. 15. The system as described in claim 11 comprising: a cycle steam network, connecting said steam source to said high pressure section, connecting an exhaust outlet of said high pressure section to said reheater cycle path, and connecting the cycle steam output recycling heater meansto the steam inlet of said low pressure section, so as to pass reheated and relatively dry steam to said low pressure section. 16. The system as described in claim 11, comprising at least one low pressure double flow turbine having two turbine sections, said reheater means comprising a. separate reheater for reheating wet steam exhausted 1 from said high pressure turbine before it is passed to each respective said low pressure section, cycle steam network comprising a separate path from said high pressure turbine through each such separate reheater to each respective low pressure turbine section.

17. The system as described in claim 11 wherein said I reheater means is an element in a closed control loop including said control means, for continuously controlling the temperature at the inlet of at least one of said low pressure sections.

18. The apparatus as described in claim 11 wherein said reheater control means comprises an electropneumatic transducer for converting electrical control signals to pneumatic signals, and reheater valve means connected between said steam source and said reheater means tov regulate passage of heating steam through said reheater'means, said electropneumatic transducer output being connected to saidreheater valve means to control the position of same, thereby controlling the amount of heating steam passing to said reheater means.

19. The apparatus as described in claim 11 wherein said mode control means isswitchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operating parameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.

20. The apparatus as described in claim 11 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature at said low pressure inlets from a first predeterminedtemperature to a second predetermined temperature along a predetermined temperature path, over a predetermined time period.

21. The apparatus as described in claim 11 wherein said reheater control means has second mode signals adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.

22. The apparatus as described in claim 11 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.

23. The apparatus as described in claim 11 wherein said reheater control means comprises a reset circuit operatively connected to control said reheater valves at a predetermined lower level of reheater valve lift. 24. The apparatus as described in claim 11 wherein said reheater control means comprises manual control circuitry permitting manual control of said reheater means when said reheater control means is in a manual mode.

25. In a turbine system for generating electrical energy, having at least one high pressure turbine and a plurality of low pressure turbines driven by a source of steam, a reheater system for reheating cycle steam which is passed throughsaid high pressure turbine before it is passed into and through one of said low pres sure turbines, comprising:

a. reheater means, receiving heating steam from said steam source for reheating relatively wet cycle steam from said at least one high pressure turbine and producing superheated and relatively dry steam suitable for passage to one of said low pressure turbines;

b. temperature detection means, for detecting turbine temperatures near steam inlets of said low pressure turbines, and generating signals representing said turbine temperatures;

0. electronic reheater control means receiving said signals, and having logic for deriving which one of said signals represents the highest of said temperatures, comparator circuitry for comparing said highest temperature signal with a temperature reference signal, and a plurality of control modes in each of which the amount of heating steam passing through said reheater means is controlled according to a separate predetermined function; and

d. mode control means, adapted for placing said control means inone of said plurality of modes.

26. The reheater system as described in claim 25 wherein said mode control means is switchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operating parameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.

27. The reheater system as described in claim -25 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature of said low pressure inlets from a first predetermined temperature to a second predetermined temperature, over a predetermined time period.

28. The apparatus as described in claim 27 wherein said reheater control means has a second mode adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.

29. The apparatus as described in claim 27 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.

30. In a turbine system, having a controllable reheater for reheating steam passed from a high pressure.

turbine to a low pressure turbine, an electronic control system having an output connected to said reheater for controlling the operation of said reheater so as to control the temperature of the steam passed to said low pressure turbine and accordingly the turbine temperature at the inlet where said reheated steam is received, comprising:

a. cold start means for generating a cold start control signal when said electronic system is switched into a cold start mode, for controlling said reheater over a fixed period of time so as to raise said low pressure turbine inlet temperature from a first predetermined temperature to a second predetermined temperature over a predetermined time period;

b. constant temperature means, for generating a constant temperature control signal when said electronic control means is switched into a constant temperature mode, said constant temperature signal automatically maintaining the temperature at said low pressure turbine inlet at a predetermined temperature;

c. hot start means, for generating a hot-start control signal to quickly raise said low pressure turbine inlet to a predetermined temperature when said electronic control system. is switched into a hot start mode;

d. reset means, for generating a reset control signal to maintain said low pressure turbine inlet at a low temperature when said electronic control system is switched into a reset mode;

e. manual control means, adapted so that said electronic control system output can be manually determined when said electronic control system is switched into a manual mode; and

f. control mode means for switchably connecting said electronic control system into one of said modes.

31. The electronic control system as described in claim 30, comprising temperature limit means, for controlling said reheater to automatically reduce the temperature of said low pressure turbine inlet by a predetermined amount when said turbine inlet temperature reaches a predetermined high temperature.

32. The electronic control system as described in claim 31, comprising computer means operatively connected to said control mode means, for automatically switching said system into one of said plurality of modes.

33. The electronic control system as described in claim 31, comprising control mode means adapted to be interfaced with a programmable digital computer, for automatic selection of the mode of control.

34. A method of electronic control of a turbine reheater system for reheatingsteam in passage from a high pressure turbine section to a plurality of low pressure turbine sections, said'reheater system being controlled by an electronic control system adaptable to op- V crate-in a plurality of operational modes, comprising:

a. sensing the temperatures in said low pressure sections, and deriving electrical signals representing said temperatures;

b. continuously auctioneering said temperature signals to obtain an auctioneered temperature signal representing the highest of said sensed temperatures; g c. continuously comparing said auctioneered temperature signal with a high temperature limit reference signal; and d. automatically initiating temperature control of said reheater system to reduce said auctioneered temperature to a first predetermined temperature differential below said high temperature limit, when said compared auctioneered temperature exceeds said temperature limit, and maintaining said temperature control until said auctioneered temperature drops below said limit by a second predetermined temperature differential. 35. The method as set forth in claim 34 comprising the steps of:

placing said electronic control system in a constant temperature mode of operation, comparing said auctioneered temperature signal with a first reference signal representing a constant temperature, deriving a control signal from said comparison, and controlling the reheater valves of said reheater system with said derived control signal to maintain the hottest low pressure section temperature at about said constant temperature when said electronic control system is in said constant temperature mode. 36.'The method as described in claim 34 comprising: placing said control system in a cold start mode of control, generating a time varying control signal, controlling said reheater'system with said time varying control signal so as to raise the temperature of said low pressure turbine sections from a first predetermined temperature to a second predetermined temperature along a predetermined path over a predetermined period of time. 37. The method as described in claim 34, comprising: placing said electronic control system in a hot start mode of control, generating a fast rise time control signal, controlling said reheater system with said fast rise time control signal so as toraise the temperature of said low pressure sections quickly to a point where said auctioneered temperature is substantially equal to a predetermined temperature reference. 38. The method as described in claim 34, comprising: placing said electronic control system in a reset mode of control simultaneously with connecting power to the electronic control system, and automatically maintaining said electronic control system in such mode until switched into another mode by an operator,in which reset mode of control the reheater system maintains said temperatures at a predetermined minimum level. 39. The'method as described in claim 34, comprising: placing said electronic control system into a computer mode of control, and automatically controlling said reheater system by a programmable computer. 40. A method of operation of a nuclear turbine systern, which system comprises a high pressure turbine section and'at least one low pressure turbine section, comprising:

a. communicating relatively hot and dry steam to said high pressure turbine section, for driving same;

b. exhausting relatively cool and wet steam, from which said high pressure turbine section has taken energy, from said high pressure turbine section;

c. reheating said relatively wet steam by bringing it into heat transfer contact with a controlled flowof heating steam;

d. communicating said reheated steam to an inlet of said low pressure turbine section, for driving said low pressure turbine section;

e. drivingan electric generator from said high pressure and low pressure turbine sections, to generate electrical power;

f. monitoring the temperature at said low pressure inlet, and generating an electrical temperature signal representing said low pressure section temperature;

' g. automatically and continuously generating a continuous electrical control signal according to one of a'plurality of control modes and operatively controlling said controlled flow of heating steam with said electrical control signal when said temperature signal is below a predetermined minimum level; and

h. choosing said one of a plurality of control modes,

thereby controlling the step of reheating and correspondingly controlling the temperature of said at least one low pressure turbine section.

41. The method as described in claim 46, comprising controlling said flow of heating steam over a fixed period of time so as to raise the temperature at said low pressure inlet from a first predetermined temperature substantially linearly to a second predetermined temperature, and over a predetermined time period.

42. The method as described in claim 40 comprising simultaneously initiating control of said heating steam and limiting said control signal to a reset level.

43. The method as described in claim 40 comprising automatically choosing the control mode of operation as a function of analysis of the turbine systemoperation made by a computer.

44. The method as described in claim 40, wherein said turbine system comprises at least two low pressure turbine sections, and comprising the step of sensing the temperature at the steam inlet of each of said low pressure sections and generating temperature signals corresponding to said sensed temperatures, and auctioneering said temperature signals to derive an auctioneered signal representing the highest of said temperatures.

45. The method as described in claim 44 comprising 'the steps of comparing said auctioneered signal with a high temperature reference signal, and controlling said reheating to lower said auctioneered temperature by a predetermined temperature differential when said auctioneered temperature is sensed to have exceeded said high temperature reference.

46. The method as set forth in claim 45 comprising the steps of locking said system out of all other modes of reheater control when said auctioneered temperature is detected to have exceeded said high temperature reference, and automatically returned said system to its prior mode of reheater control when said auctioneered temperature is lowered by a second predetermined temperature differential.

47. An electric generating system with a control subsystem for controlling the temperature of at least some of the steam utilized in powering a steam turbine, comprising: I

a steam generator providing a source of steam;

a high pressure steam turbine section and at least one low pressure steam turbine section, operatively combined to provide a turbine output;

electrical generating means, connected to and driven by said turbine output, for generating electrical energy;

means for valving a flow of steam through said steam turbine;

means for moving said valving means from one position to another;

means for sensing the magnitude of the rotational velocity of said turbine,

means connecting to said valve moving means whereby signals are transmitted from said sensing means to said valve moving means,

means for measuring the magnitude of energy flow from said electronic generating system,

means connecting said energy flow measuring means and transmitting signals to said valve. moving means, whereby said valving means is moved from one positionto another in response to the signals from said energy flow magnitude measuring means,

saidvalving means including high pressure valving means having throttle stop valving means and control valving means whereby speed and load control are accomplished during turbine startup and load phase of operation,

reheater means for heating relatively wet steam and producing super-heated, relatively dried steam, and having a heating steam path for passing therethrough heating steam and a cycle path for passing therethrough cycle steam which is reheated by said heating steam, said heating steam path being connected to said steam source;

electronic reheater control means, operatively connected between said steam source and said reheater means, to control the amount of said heating steam passing to said reheater means, and having a plurality of modes of control in each of which said heating steam is continuously controlled according to a separate function of time;

means for maintaining said control means in a selected'one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference; means for detecting a predetermined operating condition of said low pressure section;

reheater valve means operatively connected between said steam source and said reheater means to control the flow of said heating steam to said reheater means;

electrically operable actuator means with said reheater valve means;

and means for electronically controlling said actuator means in response to said detecting means to control the rate at which heating steam flow changes on the different operating conditions and to limit a predetermined operating condition of the low pressure section under at least some operating condi-. tions during which heating rate is controlled.

48. A system as described in claim 47 wherein said detecting means detects the predetermined operating temperature of said low pressure section.v

49. A system as described in claim 48 wherein means are provided for maintaining said electronic control means in a selected one of a plurality of modes of con- -trol when the last-mentioned operating condition is within the limit value. 

1. An electric generating system with a control subsystem for controlling the temperature of at least some of the steam utilized in powering a steam turbine, comprising: a steam generator providing a source of steam; a high pressure steam turbine section and at least one low pressure steam turbine section, operatively combined to provide a turbine output; electrical generating means, connected to and driven by said turbine output, for generating electrical energy; means for valving a flow of steam through said steam turbine; means for moving said valving means from one position to another; means for sensing the magnitude of the rotational velocity of said turbine; means connecting to said valve moving means whereby signals are transmitted from said sensing means to said valve moving means; means for measuring the magnitude of energy flow from said electric generating system; means connecting said energy flow measuring means and transmitting signals to said valve moving means, whereby said valving means is moved from one position to another in response to the signals from said energy flow magnitude measuring means; said valving means including high pressure turbine valving means having throttle-stop valving means and control valving means whereby speed and load control are accomplished during turbine startups and under load phases of operation; reheater means for heating relatively wet steam and producing super-heated, relatively dried steam, and having a heating steam path for passing therethrough heating steam and a cycle path for passing therethrough cycle steam which is reheated by said heating steam, said heating steam path being connected to said steam source; temperature detection means mounted relative to said low pressure section, for detecting a predetermined operating temperature of said low pressure section; and electronic reheater control means, operatively connected between said steam source and said reheater means, to control the amount of said heating steam passing to said reheater means.
 2. The system as described in claim 1 having a plurality of modes of control in each of which said heating steam is continuously controlled according to a separate function of time; and means for maintaining said control means in a selected one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference.
 3. The system as described in claim 1 comprising: a cycle stEam network, connecting said steam source to said high pressure section, connecting an exhaust outlet of said high pressure section to said reheater cycle path, and connecting the cycle steam output recycling heater means to the steam inlet of said low pressure section, so as to pass reheated and relatively dry steam to said low pressure section.
 4. The system as described in claim 2, comprising at least one low pressure double flow turbine having two turbine sections, said reheater means comprising a separate reheater for reheating wet steam exhausted from said high pressure turbine before it is passed to each respective said low pressure section, cycle steam network comprising a separate path from said high pressure turbine through each such separate reheater to each respective low pressure turbine section.
 5. The system as described in claim 2 wherein said reheater means is an element in a closed control loop including said control means, for continuously controlling the temperature at the inlet of at least one of said low pressure sections.
 6. The apparatus as described in claim 3 wherein said reheater control means comprises an electropneumatic transducer for converting electrical control signals to pneumatic signals, and reheater valve means connected between said steam source and said reheater means to regulate passage of heating steam through said reheater means, said electropneumatic transducer output being connected to said reheater valve means to control the position of same, thereby controlling the amount of heating steam passing to said reheater means.
 7. The apparatus as described in claim 2 wherein said mode control means is switchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operating parameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.
 8. The apparatus as described in claim 2 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature at said low pressure inlets from a first predetermined temperature to a second predetermined temperature along a predetermined temperature path, over a predetermined time period.
 9. The apparatus as described in claim 8 wherein said reheater control means has second mode signals adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.
 10. The apparatus as described in claim 8 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.
 11. The apparatus as described in claim 6 wherein said reheater control means comprises a reset circuit operatively connected to control said reheater valves at a predetermined lower level of reheater valve lift.
 12. The apparatus as described in claim 2 wherein said reheater control means comprises manual control circuitry permitting manual control of said reheater means when said reheater control means is in a manual mode.
 13. A reheater control system for a steam turbine electric generating system having at least one high pressure turbine section and at least one low pressure turbine section, a reheater system comprising: reheater means for controlling heating steam for reheating cycle steam, temperature detection means common for detecting turbine temperatures near steam inlets of said low pressure turbine, and generating signals representing said turbine temperatures, electronic reheater control means receiving said signals from said temperature detection means and transmitting signals to said reheater means whereby said temperatures at said steam inlets of said low pressure turbine are regulated to meet predetermined criteria.
 14. The system as described in claim 11 having a plurality of modes of control in each of which said heating steam is continuously controlled according to a separate function of time; and means for maintaining said control means in a selected one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference.
 15. The system as described in claim 11 comprising: a cycle steam network, connecting said steam source to said high pressure section, connecting an exhaust outlet of said high pressure section to said reheater cycle path, and connecting the cycle steam output recycling heater means to the steam inlet of said low pressure section, so as to pass reheated and relatively dry steam to said low pressure section.
 16. The system as described in claim 11, comprising at least one low pressure double flow turbine having two turbine sections, said reheater means comprising a separate reheater for reheating wet steam exhausted from said high pressure turbine before it is passed to each respective said low pressure section, cycle steam network comprising a separate path from said high pressure turbine through each such separate reheater to each respective low pressure turbine section.
 17. The system as described in claim 11 wherein said reheater means is an element in a closed control loop including said control means, for continuously controlling the temperature at the inlet of at least one of said low pressure sections.
 18. The apparatus as described in claim 11 wherein said reheater control means comprises an electropneumatic transducer for converting electrical control signals to pneumatic signals, and reheater valve means connected between said steam source and said reheater means to regulate passage of heating steam through said reheater means, said electropneumatic transducer output being connected to said reheater valve means to control the position of same, thereby controlling the amount of heating steam passing to said reheater means.
 19. The apparatus as described in claim 11 wherein said mode control means is switchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operating parameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.
 20. The apparatus as described in claim 11 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature at said low pressure inlets from a first predetermined temperature to a second predetermined temperature along a predetermined temperature path, over a predetermined time period.
 21. The apparatus as described in claim 11 wherein said reheater control means has second mode signals adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.
 22. The apparatus as described in claim 11 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.
 23. The apparatus as described in claim 11 wherein said reheater control means comprises a reset circuit operatively connected to control said reheater valves at a predetermined lower level of reheater valve lift.
 24. The apparatus as described in claim 11 wherein said reheater control means comprises manual control circuitry permitting manual control of said reheater means when said reheater control means is in a manual mode.
 25. In a turbine system for generating electrical energy, having at least one high pressure turbine and a plurality of low pressure turbines driven by a source of steam, a reheater system for reheating cycle steam which is passed through said high pressure turbine before it is passed into and through one of said low pressure turbines, comprising: A. reheater means, receiving heating steam from said steam source for reheating relatively wet cycle steam from said at least one high pressure turbine and producing superheated and relatively dry steam suitable for passage to one of said low pressure turbines; b. temperature detection means, for detecting turbine temperatures near steam inlets of said low pressure turbines, and generating signals representing said turbine temperatures; c. electronic reheater control means receiving said signals, and having logic for deriving which one of said signals represents the highest of said temperatures, comparator circuitry for comparing said highest temperature signal with a temperature reference signal, and a plurality of control modes in each of which the amount of heating steam passing through said reheater means is controlled according to a separate predetermined function; and d. mode control means, adapted for placing said control means in one of said plurality of modes.
 26. The reheater system as described in claim 25 wherein said mode control means is switchably connected to programmable computer means for continuously calculating the desired mode of control of said reheater control means, and comprising a data network for continuously monitoring physical operating parameters in said low pressure sections and for transmitting to said computer means data representing said monitored parameters.
 27. The reheater system as described in claim 25 wherein said reheater control means has a first mode adapted to control said heating steam over a fixed period of time so as to vary the temperature of said low pressure inlets from a first predetermined temperature to a second predetermined temperature, over a predetermined time period.
 28. The apparatus as described in claim 27 wherein said reheater control means has a second mode adapted to maintain the temperature of the hottest low pressure turbine inlet at a predetermined temperature.
 29. The apparatus as described in claim 27 wherein said reheater control means has a third mode adapted to bring said heating steam quickly to a level corresponding to a predetermined low pressure inlet temperature.
 30. In a turbine system, having a controllable reheater for reheating steam passed from a high pressure turbine to a low pressure turbine, an electronic control system having an output connected to said reheater for controlling the operation of said reheater so as to control the temperature of the steam passed to said low pressure turbine and accordingly the turbine temperature at the inlet where said reheated steam is received, comprising: a. cold start means for generating a cold start control signal when said electronic system is switched into a cold start mode, for controlling said reheater over a fixed period of time so as to raise said low pressure turbine inlet temperature from a first predetermined temperature to a second predetermined temperature over a predetermined time period; b. constant temperature means, for generating a constant temperature control signal when said electronic control means is switched into a constant temperature mode, said constant temperature signal automatically maintaining the temperature at said low pressure turbine inlet at a predetermined temperature; c. hot start means, for generating a hot start control signal to quickly raise said low pressure turbine inlet to a predetermined temperature when said electronic control system is switched into a hot start mode; d. reset means, for generating a reset control signal to maintain said low pressure turbine inlet at a low temperature when said electronic control system is switched into a reset mode; e. manual control means, adapted so that said electronic control system output can be manually determined when said electronic control system is switched into a manual mode; and f. control mode means for switchably connecting said electronic control system into one of said modes.
 31. The electronic conTrol system as described in claim 30, comprising temperature limit means, for controlling said reheater to automatically reduce the temperature of said low pressure turbine inlet by a predetermined amount when said turbine inlet temperature reaches a predetermined high temperature.
 32. The electronic control system as described in claim 31, comprising computer means operatively connected to said control mode means, for automatically switching said system into one of said plurality of modes.
 33. The electronic control system as described in claim 31, comprising control mode means adapted to be interfaced with a programmable digital computer, for automatic selection of the mode of control.
 34. A method of electronic control of a turbine reheater system for reheating steam in passage from a high pressure turbine section to a plurality of low pressure turbine sections, said reheater system being controlled by an electronic control system adaptable to operate in a plurality of operational modes, comprising: a. sensing the temperatures in said low pressure sections, and deriving electrical signals representing said temperatures; b. continuously auctioneering said temperature signals to obtain an auctioneered temperature signal representing the highest of said sensed temperatures; c. continuously comparing said auctioneered temperature signal with a high temperature limit reference signal; and d. automatically initiating temperature control of said reheater system to reduce said auctioneered temperature to a first predetermined temperature differential below said high temperature limit, when said compared auctioneered temperature exceeds said temperature limit, and maintaining said temperature control until said auctioneered temperature drops below said limit by a second predetermined temperature differential.
 35. The method as set forth in claim 34 comprising the steps of: placing said electronic control system in a constant temperature mode of operation, comparing said auctioneered temperature signal with a first reference signal representing a constant temperature, deriving a control signal from said comparison, and controlling the reheater valves of said reheater system with said derived control signal to maintain the hottest low pressure section temperature at about said constant temperature when said electronic control system is in said constant temperature mode.
 36. The method as described in claim 34 comprising: placing said control system in a cold start mode of control, generating a time varying control signal, controlling said reheater system with said time varying control signal so as to raise the temperature of said low pressure turbine sections from a first predetermined temperature to a second predetermined temperature along a predetermined path over a predetermined period of time.
 37. The method as described in claim 34, comprising: placing said electronic control system in a hot start mode of control, generating a fast rise time control signal, controlling said reheater system with said fast rise time control signal so as to raise the temperature of said low pressure sections quickly to a point where said auctioneered temperature is substantially equal to a predetermined temperature reference.
 38. The method as described in claim 34, comprising: placing said electronic control system in a reset mode of control simultaneously with connecting power to the electronic control system, and automatically maintaining said electronic control system in such mode until switched into another mode by an operator, in which reset mode of control the reheater system maintains said temperatures at a predetermined minimum level.
 39. The method as described in claim 34, comprising: placing said electronic control system into a computer mode of control, and automatically controlling said reheater system by a programmable computer.
 40. A method of operation of a nuclear turbiNe system, which system comprises a high pressure turbine section and at least one low pressure turbine section, comprising: a. communicating relatively hot and dry steam to said high pressure turbine section, for driving same; b. exhausting relatively cool and wet steam, from which said high pressure turbine section has taken energy, from said high pressure turbine section; c. reheating said relatively wet steam by bringing it into heat transfer contact with a controlled flow of heating steam; d. communicating said reheated steam to an inlet of said low pressure turbine section, for driving said low pressure turbine section; e. driving an electric generator from said high pressure and low pressure turbine sections, to generate electrical power; f. monitoring the temperature at said low pressure inlet, and generating an electrical temperature signal representing said low pressure section temperature; g. automatically and continuously generating a continuous electrical control signal according to one of a plurality of control modes and operatively controlling said controlled flow of heating steam with said electrical control signal when said temperature signal is below a predetermined minimum level; and h. choosing said one of a plurality of control modes, thereby controlling the step of reheating and correspondingly controlling the temperature of said at least one low pressure turbine section.
 41. The method as described in claim 46, comprising controlling said flow of heating steam over a fixed period of time so as to raise the temperature at said low pressure inlet from a first predetermined temperature substantially linearly to a second predetermined temperature, and over a predetermined time period.
 42. The method as described in claim 40 comprising simultaneously initiating control of said heating steam and limiting said control signal to a reset level.
 43. The method as described in claim 40 comprising automatically choosing the control mode of operation as a function of analysis of the turbine system operation made by a computer.
 44. The method as described in claim 40, wherein said turbine system comprises at least two low pressure turbine sections, and comprising the step of sensing the temperature at the steam inlet of each of said low pressure sections and generating temperature signals corresponding to said sensed temperatures, and auctioneering said temperature signals to derive an auctioneered signal representing the highest of said temperatures.
 45. The method as described in claim 44 comprising the steps of comparing said auctioneered signal with a high temperature reference signal, and controlling said reheating to lower said auctioneered temperature by a predetermined temperature differential when said auctioneered temperature is sensed to have exceeded said high temperature reference.
 46. The method as set forth in claim 45 comprising the steps of locking said system out of all other modes of reheater control when said auctioneered temperature is detected to have exceeded said high temperature reference, and automatically returned said system to its prior mode of reheater control when said auctioneered temperature is lowered by a second predetermined temperature differential.
 47. An electric generating system with a control subsystem for controlling the temperature of at least some of the steam utilized in powering a steam turbine, comprising: a steam generator providing a source of steam; a high pressure steam turbine section and at least one low pressure steam turbine section, operatively combined to provide a turbine output; electrical generating means, connected to and driven by said turbine output, for generating electrical energy; means for valving a flow of steam through said steam turbine; means for moving said valving means from one position to another; means for sensing the magnitude of the rotational velocity of said turbine, means connecting to said Valve moving means whereby signals are transmitted from said sensing means to said valve moving means, means for measuring the magnitude of energy flow from said electronic generating system, means connecting said energy flow measuring means and transmitting signals to said valve moving means, whereby said valving means is moved from one position to another in response to the signals from said energy flow magnitude measuring means, said valving means including high pressure valving means having throttle stop valving means and control valving means whereby speed and load control are accomplished during turbine startup and load phase of operation, reheater means for heating relatively wet steam and producing super-heated, relatively dried steam, and having a heating steam path for passing therethrough heating steam and a cycle path for passing therethrough cycle steam which is reheated by said heating steam, said heating steam path being connected to said steam source; electronic reheater control means, operatively connected between said steam source and said reheater means, to control the amount of said heating steam passing to said reheater means, and having a plurality of modes of control in each of which said heating steam is continuously controlled according to a separate function of time; means for maintaining said control means in a selected one of said plurality of modes of control when the temperature of said low pressure section is below a high temperature reference; means for detecting a predetermined operating condition of said low pressure section; reheater valve means operatively connected between said steam source and said reheater means to control the flow of said heating steam to said reheater means; electrically operable actuator means with said reheater valve means; and means for electronically controlling said actuator means in response to said detecting means to control the rate at which heating steam flow changes on the different operating conditions and to limit a predetermined operating condition of the low pressure section under at least some operating conditions during which heating rate is controlled.
 48. A system as described in claim 47 wherein said detecting means detects the predetermined operating temperature of said low pressure section.
 49. A system as described in claim 48 wherein means are provided for maintaining said electronic control means in a selected one of a plurality of modes of control when the last-mentioned operating condition is within the limit value. 